Gas detectors may be carried by workers and/or located throughout a work place and may detect gases in the environment. Gas detectors may be operable to alert a user and/or supervisor when a harmful gas or level of gas is detected. To ensure that gas detectors are functioning properly, the detectors may be periodically calibrated (or zeroed). Some calibration methods may involve providing purified or filtered air to the gas detector and calibrating the resulting readings to a zero reference point.